Some engine systems may include devices such as throttle turbine generators to use energy from a pressure difference across a throttle that is otherwise wasted in an intake passage of an engine. In some examples, such as shown by Leone et al. in US 20130092126, the throttle turbine generator includes a turbine mechanically coupled to a generator which may generate current that is supplied to a battery of the engine. By charging the battery with such a generator, fuel economy of the engine system may be improved. For example, the need to charge the battery with an engine driven generator is reduced.
The inventors herein have recognized that by coupling the turbine to a motor-generator, there may be conditions where the turbine may be driven by the motor. In particular, the motor-generator may be operated as a motor drawing current from a battery and rotating the turbine propeller as a compressor. In other words, the system may be operated as a turbine-driven generator or a motor-driven compressor, as required. By coupling the motor-driven compressor to a fuel vapor purge canister, during conditions when there is not sufficient intake manifold vacuum, canister purging can be achieved by drawing purge vapors using the compressor. This allows a canister purge rate to be maintained even when the intake manifold vacuum is not sufficient to maintain the desired purge rate. The compressor may alternatively be used to draw air through other vacuum requiring devices and actuators of the engine system.
In one example, a method of operating an engine system including a throttle turbine generator may comprise: selectively operating a motor-generator to rotate a turbine propeller coupled in an intake throttle bypass; and drawing fuel vapors from a fuel system canister into an engine intake manifold through the rotating propeller.
In this way, the fuel economy benefits of a throttle turbine generator are increased. By using the turbine during selected conditions to drive an electrical motor-generator, energy lost across an intake throttle can be recouped and engine operation is not necessitated for charging a system battery. By using the electrical motor-generator to drive the turbine propeller during selected other conditions, air may be drawn through a purge canister by operating the turbine as a compressor, thereby allowing canister purging even when there is insufficient manifold vacuum. By improving canister purging, and maintaining a canister purge rate over a larger range of engine operating conditions, engine exhaust emissions are improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.